Hi,

Hoping someone has encountered a similar issue or knows enough about the platform they can help me narrow down this super elusive hard start.

Car background: Well-kept 2003 automatic (gonna swap it once this is figured out...) NB, approx 75k on the odo. Kept up on maintenance after acquiring it about 5 years ago, before that owned by someone who would only take it out on the weekends for light driving. The rubber had hardened at parts, it definitely needed new motor mounts, but otherwise the car was mint. I've kept up on oil changes and maintenance like timing belts and the like.

Detail of the problem: Been hard starting for approximately one year. Takes about 8-9 cranks to turnover when cold or hot, with the exception of immediate restarts after turning off the engine. Very rarely will start up fine after sitting for a few minutes, but usually always a hard start unless the engine has just been turned off (within the last 5 seconds or so). No codes whatsoever.

Troubleshooting so far:
Replaced the fuel filter and one of the fuel lines because the quick connect fitting failed. No change in the hard start.
Replaced the battery with a brand new battery from NAPA. No change in the hard start, but cranking was stronger.
Replaced plugs with new NGK Ruthenium HX plugs along with new NGK blue wires. No change in the hard start.
Cleaned throttle body with carb cleaner. No change in the hard start.
Cleaned and checked the air intake along with replacing the air intake filter. No change in the hard start.
Replaced the crankshaft position sensor. No change in the hard start.
Replaced the coolant temperature sensor. No change in the hard start.
Replaced plugs with copper NGK V-Powers, and replaced coil packs with new NGK coils.

At this point the ability to make it turn over fine if the car had just turned off made me think more towards the fuel again. I spoke to TCM about it and was led in the direction of the injectors based on their advice, and worked to check fuel pressure and do the pinch test to determine the direction of any fuel leaking.
The car leaked from 52psi to 46psi over 2 hours when pinched off at the rail side where only the fuel pump could drop pressure, and then the car leaked from 52psi to 28psi over 2 hours when pinched off at the pump side (only the injectors could drop pressure). I determined it had to be the injectors leaking fuel at this point.

I ordered a cleaned set of OEM injectors from TCM with flow certification and put them in. No change in the hard start.
The car threw a P0340 code and refused to start. Double-checked in the engine bay and I had forgot to plug in one part of the VVT assembly, which I plugged in. The car then decided to start. (hard).

I thought maybe I put everything back together wrong and there was a vacuum leak, so I sprayed a bit of starter fluid at all the possible vacuum leak locations and idle held steady and there were no leaks.

I figured at this point it probably had to be the fuel pump failing to provide pressure quickly enough.

I changed the fuel pump with the Delphi FE0415 and replaced the FPR with a Delphi FPR too. It fluked and started on the second crank, and I was so happy until I checked later. No change in the hard start.

Checked the battery and starter somewhat - battery cranking volts are 11.6 and jump starting the car to give it extra juice has no effect on the hard start either.

At this point I have no idea what it could be. I think probably only the starter or the camshaft position sensor. Any ideas? Anyone been here?

 

If you give it a little throttle, does it start better?

If you spray some starting fluid into the intake before cranking, will it fire right up every time?

What does it idle at once started?

What RPM does it idle at when fully warmed up?

Can you plug into the ECU with a scanner/OBD II tool and see what AIT/CLT the ecu is reporting?

Video of the problem starts?

 

Not with the car right now and won't be for a few days, but can answer some of these:

-More throttle doesn't improve it at least last I checked approx 6 months ago
-Haven't tried starter fluid yet
-Idles at approximately 1000-1100 rpm once started
-Fully warmed up ends up idling at approximately 8-900rpm, idle is very smooth
-Can check the ECU in a few days
-No video right now

 

Just got back out to the car and replaced the starter with a BOSCH remanufactured one from TCM. Cranks crazy strong but still the same issue. For anyone reading this, endeavor to try and not replace the starter or do it while you're doing transmission work/have the engine apart because accessing that third bolt holding it on the driver's side with everything put together is miserable, you have to come at it with multiple extensions and wobble sockets from nearly the middle of the car, and you'll want a helper to see the bolt from the top and help guide the socket. Going to answer the rest of patsmx5's questions tomorrow.

 

Attached is a video of the problem start, the gauge cluster and the engine running.

Confirmed throttle does NOT help it start, and starter fluid sprayed into the intake makes it sputter and die and hesitate instead of starting cleanly after a hard start like in the video.

 

Ok, that helps. So from the video, it looks like it runs perfect once it decides to run. First guesses would be cam sensor or crank sensor. Since you replace crank sensor already, perhaps try the cam sensor.

Few things I'd like to try to rule some things out. This needs to be done when cold, so you know it will give a hard start.

Unplug the fuel pump. Pull the fuse or relay for the injector so they don't fire either. Then spin it over for 20 seconds non-stop, and watch to see that you get oil pressure for a few seconds while doing this. It won't start since no fuel. Then key OFF, Then quickly reconnect the injector fuse and fuel pump wires, then Key ON, and try to start. See if it still hard starts or starts properly as it should.

 

Sounds good, thank you. I have a new NTK cam sensor coming from RockAuto I will replace and see if that helps, and I will do the fuel test ASAP. When you say unplug the fuel pump, do you mean at the top of the tank or do you mean the relay above the throttle? If so, can you show me exactly which relay it is? No picture online is clear at all. I've been just disconnecting a fuel hose to relieve system pressure.

 

Should be the ENGINE fuse in the interior fuse box for the fuel pump and the FUEL INJ fuse under the hood glove box for the injectors.

 

If you can just unplug the fuel pump connector at the tank, that's what I would do. So nothing else is messed with.

 

Got the parts in from RockAuto.

Replaced the cam position sensor, the throttle position sensor, and the main relay. No dice; and I used quality parts too.

Then did as you asked; oil pressure gauge comes online to read about halfway at the 10 second mark, then remains there for the rest of the cranking period. No dice there either, it seemed to start a BIT faster to me but it was still taking longer to start then it should.

 

Checked proprietary shop manuals for the issue and it doesn't seem to have any listing for this problem that I haven't already tried. Is it possible that the way the fuel pump doesn't prime on the miata until the key is ON causes hard starts in some vehicles?

 

You can put a fuel pressure gauge on the car, set it on the windshield so you can see it, and then start the car while filming the dash/fuel pressure gauge.

 

Right, I did that before with an in-line fuel gauge and a helper and fuel goes straight up when starting and holds steady at 60psi. Is there anything else I can try? What about the oil pressure thing you had me do?

 

The oil pressure thing was to check the cam timing effect on startup. If you spin it over, it will give oil to the VVT actuator. I wanted to see if priming that had an effect. If it did, that would point to cam timing as contributing, explaining why cold starts were particularly affected.

So far it sound like you're getting fuel.

Do you have a timing light? If so, you can use it to check if you have spark when the hard start occurs.

 

Awesome thanks.

Yes, and I checked for timing and cylinder 1’s timing and spark are right on the money.